The news comes less than one week after Liberal MP Wajid Khan defected to the Conservatives.

The 50-year-old Lapierre will be out of politics by the end of January to join Montreal's TVA television network, where he will co-host a weekly politics show with reporter Paul Larocque.

"I announced months ago that I was going to leave and that I was not going to run again," Lapierre told CTV Newsnet.

"In the meantime, I have started my career transition ... and you know how it is in this business -- you've got to be there for the season, because if you miss a season you may miss the job totally."

He added that "we're maybe only weeks away from a federal election, so I don't think I should miss that opportunity.

Lapierre's resignation, combined with Khan's decision to cross the floor last week, gives the Conservatives a two-seat cushion, assuming Prime Minister Stephen Harper can reach an agreement with NDP Leader Jack Layton for the party's support on key legislation.

But Lapierre denied that his absence will have any political consequences for the Liberals.

"It doesn't change anything -- the dynamics in the House won't change because of me," he said.

Lapierre rejoined the Liberal party in 2004 at the urging of former prime minister Paul Martin after a 10 year hiatus from politics.

He had defected from the Liberals to the separatist Bloc Quebecois in the early 1990s before being wooed back by Martin.

The former transport minister announced in December that he wouldn't be running in the next federal election.

"Given that I am 50 years old, I told myself it is now or never if I want to have another career," he said at the time, insisting his decision had nothing to do with Stephane Dion's election as Liberal leader.

His announcement leaves the Montreal riding of Outremont open. Many have speculated that Justin Trudeau is making a bid for the seat, though he has not confirmed the rumours.

Former prime minister Pierre Trudeau's eldest son joined the Liberal riding association in Outremont about two months ago, Montreal's La Presse newspaper reported this week.

But the newspaper reported that Dion was planning on reserving the riding for high-profile candidates who could help rebuild the party's support in Quebec.

According to the newspaper, Dion has made it clear to some Liberals that the 35-year-old Trudeau is not the star candidate he was seeking.

Trudeau has declined to comment.

Outremont has been a federal Liberal stronghold since 1935, except for a single Progressive Conservative win in 1988.

Still, Liberal support saw a considerable drop during the time Lapierre held the riding.

Trudeau lives in the adjacent riding.

With Lapierre's exit, the new standings in the 308-seat House of Commons will be: Conservatives 125, Liberals 100, Bloc Quebecois 51, NDP 29, and two independents; Speaker Peter Milliken is a Liberal.